The Trump administration announced tighter screening and security measures Friday at airports in Britain, Japan and other countries whose citizens are allowed entry into the United States without obtaining visas before they travel.
Travelers probably won't notice any immediate changes under the new standards, which are aimed at improving screening procedures at airports in the 38 countries involved in the visa waiver program.
About 20 million people a year now travel to the United States under the program, which permits stays of up to 90 days without a visa.
Department of Homeland Security officials said they also want to crack down on visitors who abuse the program by staying longer than 90 days. Last year, more than 500,000 visitors didn't leave as required, though only about 147,000 came from visa waiver countries, officials said.
If more than 2% of a nation's travelers don't leave on time, their country might have to establish a public education program for its citizens, the department said.
Four of the 38 countries now exceed that 2% standard – Hungary, Greece, Portugal and San Marino, a tiny state inside Italy, authorities said.
Since his first days in office, Trump has moved to restrict access to the U.S. on grounds of protecting the country from terrorists. The administration has moved to implement travel bans, mostly targeting Muslim countries, although court challenges to those orders are continuing.
In remarks Friday at the FBI Academy in Quantico, Va., Trump repeated his call to end a visa lottery and the system that gives priority to reuniting family members in favor of a merit-based visa system.
"You think the countries are giving us their best people?" Trump said. "They give us their worst people. What a system, the lottery system."
In announcing the new standards, Homeland Security officials said the heightened security measures were not prompted by any specific terror incidents or threats.
Countries that don't comply might be suspended from the visa waiver program, or face other penalties. But officials said they don't expect any problems, describing the 38 countries as "our closest partners" in screening out terror threats.
Under the new rules, visa waiver countries will have to begin using U.S. information on suspected terrorists and criminals to screen travelers entering their countries from elsewhere. The U.S. already shares those databases with these countries, officials said.
The rules will also require airports that send travelers to the U.S. to effectively screen their own employees to keep out suspected terrorists.
"The United States faces an adaptive and agile enemy, as terrorists continue to explore ways to reach our country and to direct, enable and inspire attacks against us," said Kirstjen Nielsen, Homeland Security secretary. "It's critically important we stay ahead of these threats by improving our security posture."